1. Field of the Invention
This invention relates to an elastomer display device which can display a pattern which can be discriminated by the naked eye by utilizing elastic deformation of an elastomer produced upon application of an electric voltage thereto. Provision is made of four laminated coatings consisting of a transparent electric conductive membrane pattern to be displayed, an elastomer coating, a metal reflecting coating and an electric conductive elastomer coating superimposed one upon the other in the order if mentioned on a glass substrate and if an electric voltage is applied between the transparent electric conductive membrane pattern and the electric conductive elastomer coating. The surface portion of the elastomer coating which is opposed to the transparent electric conductive membrane pattern is deformed into frost-shaped indentations. Light incident through the glass substrate upon the frost-shaped indentations is irregularly reflected to produce light diffusion phenomenon which allows the pattern to be discriminated by visual observation with the naked eyes.
2. Description of the Prior Art
A conventional elastomer display device is composed of a glass substrate and four coatings consisting of a transparent electric conductive membrane pattern to be displayed, an elastomer coating having a volume resistivity of the order of 10.sup.15 .OMEGA.cm, metal reflecting coating and an electric conductive elastomer coating superimposed one upon the other on the overall surface of the glass substrate so as to cover the overall surface of the pattern to be displayed. If an electric voltage is applied between the transparent electric conductive membrane pattern and the electric conductive elastomer coating, that surface portion of the elastomer coating which is opposed to the pattern to be displayed is deformed into frost-shaped indentations. A light incident through the glass substrate upon the elastomer coating is irregularly reflected by the surface deformed portion of the elastomer coating thus enabling the pattern to be displayed to be discriminated by naked eyes.
In such elastomer display device, in order to obtain contrast which is sufficient to clearly discriminate the pattern to be displayed by naked eyes, it is necessary to drive the device by applying a voltage of 80V to 100V. This driving voltage is dependent on the thickness of the elastomer coating and it is required to apply 5 KV to 10 KV per 1 mm of the thickness of the elastomer coating. As a result, in order to make the driving voltage small, the thickness of the elastomer coating must be made thin. As is well known, if the thickness of an elastomer coating formed of organic substance is made thin, pinholes exist in the thin elastomer coating which tend to induce insulation breakdown. Thus rendering the operation of the display device then becomes impossible. In addition, the wider the area to be displayed, the larger the probability of generating the pinholes. As a result, it is necessary to increase the lower limit of the thickness of the elastomer coating in dependence with the area to be displayed.
For the above described reasons, the conventional elastomer display device has the fatal disadvantages that high driving voltages are required, that the use of an elastomer coating of large thickness limits the construction of the circuit for operating the display device, and that the high driving voltage and the total volume of the elastomer coating render it impossible to widely use the display device.
In addition, for the purpose of making the driving voltage as small as possible provision has heretofore been made of a display device comprising an elastomer coating having such lower limit of thickness that its insulation breakdown does not occur. Such display device can prevent the insulation breakdown of the elastomer coating, but has the disadvantage that there is a risk of leakage current occurring and consuming a large amount of current.
In the conventional display device in which the elastomer coating, metal reflecting coating and electric conductive elastomer coating are superimposed one upon the other on the overall surface of the glass substrate, the electric field produced between the transparent electric conductive membrane pattern and the electric conductive elastomer coating becomes extended beyond the pattern to be displayed which blurs the outer peripheral portion of the pattern, thereby significantly deteriorating the resolving power of the display device.
In addition, in the conventional display device, an electric conductive elastomer coating having a high volume resistivity of the order of 10.sup.3 to 15.sup.3 .OMEGA.cm is used as an opposed electrode, so that it is difficult to uniformly and effectively apply the voltage to the overall surface of the pattern to be displayed.